In general the present invention relates to rotational drive assemblies equipped with electromechanical means for extending electrical signals between the relatively rotating components of the assembly.
More particularly, the present invention is directed to high speed rotational assemblies such as employed in centrifuges which are designed to drive a rotor at speeds of up to and exceeding 10,000 rpm. The most successful high speed centrifuges capable of speeds in excess of 10,000 rpm employ a relatively small diameter, elongate, flexible drive shaft sometimes referred to as a quill shaft because of its ability to flex and bend to accommodate various operating conditions.
One of the operating conditions which requires this flexibility in the drive shaft exists as the shaft and rotor driven thereby pass though "critical" speeds at which vibrational resonance takes place. At these critical speeds the rotational system enters into a mechanical resonance which creates such vibration that the drive shaft must be sufficiently resilient and flexible to absorb the vibrational energy.
Furthermore, it is many times difficult if not impossible to precisely balance the center mass of the rotor and shaft assembly such that it coincides with the nominal axis of rotation, that is the axis of rotation at the driven end of the quill shaft. This is particularly true when test objects of diverse size, shape and weight are attached to the rotor of the centrifuge. If the center mass of the rotor with the test device attached thereto and the shaft taken as a complete unit is displaced from the nominal axis of rotation, it is necessary for the drive shaft to accommodate the vibration caused by this unbalance. Moreover as the speed of the assembly passes through a critical speed at a high rpm, the rotor and shaft assembly automatically realigns itself above this critical speed so that the otherwise displaced center of mass coincides with the nominal axis of rotation. In order to provide this automatic realignment, the quill shaft must bend slightly. Typically, the shaft will assume a slight "S" shape as the center mass is realigned. Although more than one resonance speed may be exhibited by the assembly, in the embodiment disclosed herein the assembly has exhibited a relatively low level critical speed in the range of 900 rpm, and a relatively high critical speed in the neighborhood of 9,000 rpm. The above-mentioned realignment of the center of mass for the rotor and shaft unit takes place as the system exceeds the higher critical speed.
Centrifuges and other high speed rotating apparatus constructed with such a quill shaft operate very successfully. However, it is many times desirable to provide such a high speed rotational drive and at the same time conduct electrical signals between a stationary support for the drive and the rotated assembly. For example, the use of centrifuges to test electronic devices and components while under actual electrical operation requires such an arrangement.
Of course, there are several known electromechanical techinques for transmitting electrical signals between relatively moving parts. Perhaps the most common of these techniques is the use of a slip ring assembly in which transmission is provided by engagement of brushes against a relatively rotating electrically conductive ring or rings. Heretofore, however, the use of a slip ring assembly or other known electromechanical means for transmission of electrical signals through a rotational coupling has not been practical for high speed assemblies requiring the use of quill drive shafts.
Accordingly, it is a general object of the present invention to provide for the transmission of electrical signals, particularly multiple signals requiring plural conductors, between the stationary support of a quill shaft spindle assembly and the rotor driven by the quill shaft. Such an apparatus is useful for example in centrifugal testing of electrically operated devices and components, enabling the device to be subjected to high centrifugal and acceleration forces while under actual electrical operation.
Briefly, this object of the present invention is achieved by an apparatus in which one or more electrical wires or conductors are mounted so as to rotate with and extend in longitudinal adjacency to the flexible guill drive shaft. A plurality of washer or wafer-like conductor support members are coaxially stacked on the drive shaft and formed with radially offset and longitudinally aligned openings to support the conductors. These support members are formed from a material which is preferably slightly compressible, self-lubricating and sufficiently strong to withstand the pressure created by the wires in their attempt to fly radially outwardly from the shaft under the large centrifugal forces. Moreover these washer-like support members tend to slip on each other as the shaft bends so as to not constrain or stiffen the essential flexibility of the drive shaft at and above the critical speeds.
To enable these longitudinally extending wires to rotate with the shaft, electromechanical means is provided, such as a slip ring assembly rotating coaxially with the drive shaft adjacent an end thereof remote from the rotor. Adjacent this same end, a rotational drive means is provided for rotating the quill shaft. At the opposite end of the quill shaft, the longitudinally extending conductors pass from the aligned openings of the wafer-like support members to the rotor and are available thereat for connection to the electrical device under test.
It is observed that a more direct solution to the problem presented here would be to pass the longitudinally extending conductors up through a central hollow opening in the quill shaft. However, this is not practical because of the necessity of providing a quill shaft which exhibits the qualities of high tensile strength and flexibility. These requirements are most successfully and reliably provided by a solid, relatively small diameter spring steel shaft as disclosed more fully herein. A hollow shaft capable of accepting a number of conductors centrally thereof is not capable of realizing the same characteristics as the narrow, high tensile solid steel shaft used in the present invention.
These and further objects and various advantages of the apparatus according to the present invention will become apparent to those skilled in the art from a consideration of the following detailed description and appended drawings of an exemplary embodiment thereof.